1. Field of the Invention
The present invention relates to a combustion pressure data collection system for a multi-cylinder engine for collecting combustion pressure data of respective cylinders by measuring a combustion pressure of each cylinder.
2. Description of the Related Art
At present, internal combustion engines including automobile engines have been required to improve a combustion efficiency to reduce CO2 as well as to reduce harmful exhaust emissions for global environmental protection. In contrast, the automobile engines are used particularly in a wide range of engine rotations (RPM) such as those at a start of the engine, in an idling state, and in traveling at a low to medium speed and at a high speed as well as in a wide range of load conditions, and the like. Accordingly, the automobile engine must be controlled optimally assuming all the states of the engine described. For this purpose, in general, there has been developed an art for optimizing an engine control by measuring and analyzing a change of a combustion gas pressure using a sensor for measuring a combustion state of the engine as a means for confirming whether or not the engine is controlled properly.
That is, it is possible to correct the combustion gas pressure to an optimum pressure at all times by automatically controlling the engine optimally by an engine control system for measuring the combustion gas pressure in each cylinder. Accordingly, the engine can be controlled in accordance with a state in which it is used as well as can be controlled optimally at all times even if there are small differences due to allowable tolerances among respective engines or among respective cylinders or even if performance of the engine changes due to partial changes of respective units of the engine which are caused by using the engine for a long time, thereby the combustion efficiency can be improved to reduce CO2 and to reduce harmful exhaust emissions.
A pressure sensor (cylinder pressure sensor) using a piezoelectric device as disclosed in, for example, Japanese Patent No. 3123798 is generally used as a sensor for measuring the combustion pressure. In this case, a charge amplifier is generally used as an amplifier circuit for converting a charge signal generated by the piezoelectric device into a voltage signal and using the voltage signal as an input signal for controlling the engine.
In a multi-cylinder engine, it is preferable to provide cylinder pressure sensors for measuring combustion pressures with the respective cylinders and to optimally control the respective cylinders by measuring the combustion pressures of the respective cylinders in respective cycles in order to derive a full performance thereof, to improve a combustion efficiency for reducing CO2 gases and to reduce harmful exhaust emissions.
However, when signals outputted from the cylinder pressure sensors attached to all the cylinders are measured, a charge leakage between a piezoelectric device and a charge amplifier, an individual difference among the cylinder pressure sensors, and a change of output signal due to a temperature change must be taken into consideration. Accordingly, not only a large load imposes on an engine controller but also the controller becomes complex and increases a size thereof as well as mating steps between the pressure sensors and the controller, and the number of wirings between the cylinder pressure sensors and the controller are increased. That is, in general, the cylinder pressure sensor for measuring the combustion pressure is disadvantageous in handling thereof due to a structural complexity thereof including many circuits, and thus a cost is largely increased to utilize the cylinder pressure sensor together with a main body thereof.